The present invention is related to a power operated gear change assembly for bicycles, of the type comprising a gear change having a plurality of sprocket pinions, arranged coaxially to one another, having different diameters and selectively engageable by an endless chain; a derailleur displaceable into a plurality of positions each corresponding to engagement of the chain with a respective sprocket pinion; a powered actuator for performing displacement of the derailleur through said plurality of positions; manual control means for controlling said actuator; detecting means for detecting displacement of the derailleur; and control means operatively associated to said detecting means for controlling the operation of said actuator, and wherein the powered actuator is a d.c. electric motor with associated power supply accumulator.
A gear change assembly of the above specified type is known for instance from EP-A-0529664, according to which the electric motor operates the derailleur of the gear change through a Bowden-cable flexible transmission. A similar system is also provided for operating a front derailleur, associated to a series of sprocket wheels, which is also employing an electric motor connected to the front derailleur through a Bowden-cable transmission. The two electric motors are provided with fittings for securing thereof to the frame of a bicycle.
This arrangement has several drawbacks: firstly the mounting of the assembly, and in particular of the motor-driven actuators of the rear and front derailleurs, requires relative long and delicate operations, in particular as far as the adjustment of the respective flexible cable transmissions is concerned.
Secondly, since in practice the two derailleurs of the assembly have a conventional structure, i.e. with respective return springs, the power required for displacement thereof is relatively high, which involves employing motors and associated power supply accumulators having a relatively large size, and thus relatively heavy.
Lastly the size itself of the motors and of the accumulators, as well as their positioning on a bicycle frame, involve troublesome encumbrances and protrusions.
The above drawbacks are particularly critical in case the known motor-driven gear change assembly is applied on racing bicycles, which require simple and quick adjustments and, above all, as reduced as possible weight and encumbrances.
It is also known from DE-A-39 38 454 an assembly of the above-referenced type, which gives a partial solution to the problem related to the encumbrance of the power operated assembly, by virtue of the fact that the motor-driven actuator is directly carried by the rear derailleur. While the traditional return spring of the derailleur, and thus the relative reaction force, can be accordingly suppressed, the power operated system contemplated in this case is of electric-hydraulic type, which involves employing auxiliary equipment and, consequently, a complicated construction together with weight and encumbrance even greater than in the case of the previously described known solution. Moreover this arrangement involves precision problems in connection with the system for detecting the derailleur displacements.